As the demand for diesel boiling range fuel increases worldwide there is increasing interest in sources other than crude oil for producing diesel boiling range fuel and diesel boiling range fuel blending components. One such renewable source is what has been termed biorenewable sources. These renewable sources include, but are not limited to, plant oils such as corn, rapeseed, canola, soybean and algal oils, animal fats such as inedible tallow, fish oils and various waste streams such as yellow and brown greases and sewage sludge. The common feature of these sources is that they are composed of glycerides and Free Fatty Acids (FFA). Both of these classes of compounds contain aliphatic carbon chains having from about 8 to about 24 carbon atoms. The aliphatic carbon chains in the glycerides or FFAs can be fully saturated, or mono, di or poly-unsaturated.
There are reports in the art disclosing the production of hydrocarbons from oils. For example, U.S. Pat. No. 4,300,009 discloses the use of crystalline aluminosilicate zeolites to convert plant oils such as corn oil to hydrocarbons such as gasoline and chemicals such as para-xylene. U.S. Pat. No. 4,992,605 discloses the production of hydrocarbon products in the diesel boiling range by hydroprocessing vegetable oils such as canola or sunflower oil. Finally, US 2004/0230085 A1 discloses a process for treating a hydrocarbon component of biological origin by hydrodeoxygenation followed by isomerization.
Applicants have developed a process which comprises one or more steps to hydrogenate and deoxygenate (via catalytic decarboxylation, decarbonylation and/or hydrodeoxygenation) the feedstock. Sulfur containing components may be naturally present in the feedstock or may be added to the feedstock or the reaction mixture for various different purposes. Carbon dioxide and water are generated in the reaction zone and need to be at least partially removed from the reactor effluent prior to recycling any excess hydrogen back to the reaction zone. The effluent from the reaction zone is separated into at least a vapor portion and a liquid portion through, for example, cooling and separating. At least some of the liquid portion may be recycled to the reaction zone. The vapor portion is treated using an amine absorber solution to remove at least the carbon dioxide and optionally the sulfur component such as hydrogen sulfide so that the remaining hydrogen can be recycled back to the first reaction zone. The separated carbon dioxide and the separated hydrogen sulfide may be used for other purposes. Optionally, a selective separation unit such as a hot high pressure hydrogen stripper may be employed to selectively separate the majority of the hydrocarbon liquid portion from the vapor portion of the effluent and some of this hot, high pressure hydrocarbon liquid portion may be recycled to the reactor. The vapor portion is then cooled to separate any water.